Dental Cements

CEMENT

DEFINITION A substance that hardens to act as a Base, Liner, Filling material or Adhesive to Bind Devices and Prosthesis To Tooth Structure or To Each Other . (Anusavice)

Ideal properties of dental cements

Should be strong and hard. Able to protect pulp Should be insoluble in saliva & liquids taken in mouth.

Should be dimensionally stable. Should be adhesive . Should be non porous . Should be biocompatible and non irritant. Co-efficient of thermal expansion should be equal to the tooth

structure. Should not be affected by thermal changes and moisture. Should be easy to manipulate.

CLASSIFICATION

Based on Ingredients & Application (Craig 12th edition) Water based cementso Glass & Resin modified glass ionomer o Zinc Polycarboxylateo Zinc Phosphate

Resin based cementso Composite & adhesive resin o Compomers

Oil based cementso Zinc Oxide Eugenolo Non Eugenol -Zinc Oxide

Applications of Dental Cements• Dental Cements have both temporary and permanent

applications:i. Luting ii. Liningiii. Cementing Orthodontic appliancesiv. Fissure sealantsv. Root filling materialsvi. Temporary fillingsvii. Permanent fillingsviii. Core build-up

Zinc Oxide Eugenol

Extensively used in dentistry since 1890’s .

Least irritant of all the dental materials.

Poor strength when compared to zinc phosphate.

It has sedative effect on exposed dentin.

ZnO Principal Ingredient

White rosin Brittleness of set cement

Zn acetate Accelerator strength – up to 1%

MgO Modifier

Zn stearate Plasticizer

Eugenol Reacts with ZnO

Olive Oil Plasticizer (85% Eugenol)

Water Initiator

Acetic acid/alcohol

To accelerate setting – about 1%

POWDER LIQUID

CLASSIFICATIONType I ZOE: For temporary cementationType II ZOE: Permanent CementationType III ZOE: Temporary filling and thermal baseType IV ZOE: Cavity Liners

ZOE cement is available as

Powder and liquid orTwo – paste system

SETTING REACTION In the First Step Hydrolysis of Zinc Oxide to its hydroxide takes place . Water is essential for the reaction (dehydrated zinc oxide will not react with dehydrated eugenol )

ZnO + H2O →Zn (OH)2

The reaction proceeds as a typical acid – base reaction

Zn (OH)2 + 2HE → ZnE2 +2H2O(Zinc hydroxide)( Eugenol)- (Zinc eugenolate )

The Chelate formed is an amorphous gel that tends to crystallize imparting strength to the set mass. Structure of set cement: The set cement consists of particles of zinc oxide embedded in a matrix of zinc eugenolate. Setting time is around 4-10min.

Formulation Modifications• Plain unmodified ZOE will set very slowly;Therefore, modifications:Zinc acetate dihydrate is much more soluble than

Zn(OH)2 and will supply zinc ions more rapidly.Acetic acid catalyses the reaction faster than water

does because it increases the formation rate of Zn(OH)2.

FACTORS AFFECTING SETTING TIME Particle size: Smaller zinc oxide particles set faster Powder to liquid ratio: Higher the ratio, faster the set Addition of accelerators, e.g. alcohol, glacial acetic acid and water makes the cement set faster. Cooling the glass slab: Slows the reaction The set can be retarded by addition of glycol and glycerine which act as retarders.

MANIPULATION Power – Liquid System Powder/liquid ratio: 4:1-6:1 wt% Measured quantity of powder and liquid are dispensed onto a cool glass slab. The bulk of the powder is incorporated into the liquid and saturated thoroughly in a circular motion with a stiff bladed stainless steel spatula. Smaller increments are then added until the mix is complete.Mixing time: 60 seconds.Working time: 3 minutes.Setting time: 3.5 – 4.5 minutes.

The pH is approx. 7 at the time of placement, which makes ZOE the least irritating of all dental materials.A TF lasts approximately 3 months .

PROPERTIESCompressive strength – relatively weak cements ranges from a low of 3 to 4 MPa up to 50-55 MPa.Tensile strength – ranges from 0.32 to 5.3MPaModules of elasticity – 0.22 to 5.4GPaThermal properties – excellent thermal insulating properties Solubility and disintegration – The solubility of the set cement is highest ,they disintegrate in oral fluidsAdhesion – they do not adhere well to the enamel and dentin. This is one reason why they are not often used for final cementation of crowns and bridges.Biological properties.PH and effect on pulp (pH is 6.6 to 8) they are the least irritating of all cements. Pulpal responses are mild.They have soothing effect on the pulp.

TWO PASTE SYSTEMEqual lengths of each paste are dispersed and mixed until a uniform colour is observed.

MODIFIED ZINC OXIDE EUGENOL CEMENTSThe modified ZOE cements are as follows: EBA- alumina modified cements Polymer reinforce ZOE cementThese were introduce to improve the mechanical properties of zinc oxide eugenol cement.

Modifications of ZOE Cements1. Resin Modification• Hydrogenated resin (29%) is added to the powder.• 10% polystyrene is added to the liquid.• Other cements have 20% PMMA added .

2 Ethoxybenzoic Acid (EBA) Modified ZOE • Substitutes a part of Eugenol liquid with

orthoethoxybenzoic acid: 37.5% Eugenol : 62.5 % EBA• Fused quartz/alumina is added to ZnO.• Purpose: higher compressive strength (90MPa) and

abrasion resistance.• For strong cement set, P:L Ratio = 7:1.• Lower solubility.• Can also be used for permanent luting.

3 Eugenol Free ZnO Cements• Especially for patients allergic to Eugenol, or • For use as lining under composites/compomers.• May contain vanilate esters in place of the

Eugenol component.

4 Other Modifications• Formulation containing powder made of of 20 wt%

to 40 wt% of fine polymer particles and Zinc oxide particles that have been treated with carboxylic acid.

• The rationale is also to improve strength and abrasion resistance.

• The liquid used in this system is Eugenol.

Advantages: Minimal pulp reaction. Good sealing properties Strength adequate for lining material & luting single restoration

& retainers, with good retention form.

Disadvantages: Hydrolytic breakdown under exposure to oral fluids Inflammatory reaction in soft tissue potential allergic response Minimal mechanical properties for luting May soften & discolor

Calcium Hydroxide INTRODUCTION Herman in 1920 introduced

Ca(OH)2 Ca(OH)2 is a white odorless

powder It is strongly alkaline with a

PH of 12.5 It is classified as an

astringent in Pharmacology.

compositionAcelerator paste• Alkyl salicylate (iso-butyl salicylate or 1-methyl

triethylene salicylate)• Inert fillers – titanium oxide 12-14%• Radiopacifer – barium sulphate 32-35%• Calcium tungstate or calcium sulphate 14-15%

Base paste• Calcium hydroxide 50-60%• Zinc oxide 10%• Zinc stearate 0.5%• Ethylene toluene sulphonamides and paraffin oil

39.5%

Setting Reaction• Alkyl salicylate is chelating agent. On mixing this

with paste containing zinc oxide and calcium hydroxide, amorphous calcium disalicylate is formed.

• The sulphonamide compound used in the paste is used as a carrier.

• Some cements contain paraffin oils instead of sulphonamides. These elements are more hydrophobic and release their calcium hydroxide more slowly. .

• The Calcium hydroxide is present in stoichiometric excess.

Manipulation• Equal amount of base and catalyst dispensed on an

oil impervious paper-pad.• Mix to homogenous color.• Apply on dentine as a lining.

Mixing time: 5-10 secondsWorking time: 30 secondsSetting time: 1 minute

Properties• Basic cement; pH : 11 – 12; used to neutralize acidic cements,• Ideal to inhibit microbes esp. those found in carious dentine. • Poor mechanical strength -• Compressive Strength : 8.3 to 10.3 MPa • Tensile strength: 10 MPa• Modulus of elasticity: low -0.37 Gpa/m2

• pH: high alkaline: 9.2 to 11.7 • Setting time: 2.5 – 5.5 minutes(powder form)• Solubility and disintegration: solubility is high 0.4 to 7.8%

• High solubility in water.

MECHANISM OF ACTION• High alkaline PH(11-13) Causes neutralization of acids

produced by microorganisms. • Antibacterial effect due to high PH.• Seals the dentinal tubules offering dentin protection.• Induces reparative dentin below existing dentin.• Biocompatibility & calcific barrier enabling to maintain

pulp vitality. • Ca(OH)2 maintains a local state of alkaline by that is

necessary for bone/dentin formation .

• Stimulates formation of reparative dentine and so is applied in instances of pulpal exposure (direct pulp-capping), or near pulpal exposure (indirect pulp-capping).

• Due to its high pH, it causes irritation to the pulp.• Necrosis of cells adjacent to the cement, and

transformation of mesenchymal cell into odontoblasts which start laying down reparative dentine.

Mode of supply• Can be supplied in powder form

– powder can be mixed with distilled water, saline solution to form a thick paste and applied as such.

• Can be supplied as two paste system, one base paste another catalyst paste.

• Can be supplied as single paste (visible light).

USESAS A LINER

The calcium hydroxide pastes are now in general use as lining materials. Their perceived advantages, in addition to their therapeutic effects are as follows:• They have a rapid initial set in the cavity under the

accelerating effect of moisture.• They do not interfere with the setting reaction of the Bis-

GMA resins.• It is generally considered that the initial set of the material

in thin sections is sufficiently hard to resist the applied condensation pressures that are required even for the lathe cut amalgam alloys.

AS A BASE AND SUBBASE

Calcium hydroxide can be used both as a sub base and as a base. It should be placed deep in deep portions of the cavity preparation subsequently covered by a definitive supporting base.

• It helps in repair of pulpal tissue • It provides chemical insulation • It replaces the lost portion of the dentin.• Calcium hydroxide bases are of relatively of low strength when

compared to the other bases. These bases are used only for their therapeutic benefits, chemical insulation or for retaining the sub bases.

AS AN INTRACANAL MEDICAMENT• plays a major role as an inter-visit dressing in

the disinfection of the root canal system. • Calcium hydroxide is normally used as slurry of

Calcium hydroxide in a water base. • At body temperature less than 0.2% of Calcium

hydroxide is dissolved into ca++ and OH- ions. • Calcium hydroxide needs water to dissolve.

Therefore it is most advantageous to use water as a vehicle for the Calcium hydroxide paste

Advantages of Calcium hydroxide• Initially bactericidal then bacteriostatic. • Promotes healing and repair. • High pH stimulates fibroblasts. • Neutralizes low pH of acids. • Stops internal resorption. • Inexpensive and easy to use.

Disadvantages of Calcium hydroxide:

• Does not exclusively stimulate dentinogenesis. • Does exclusively stimulate reparative dentin. • May dissolve after one year with cavosurface

dissolution. • May degrade during acid etching. • Marginal leakage with amalgam condensation. • Does not adhere to dentin or resin restoration

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